Abstract
We characterized the spatial and temporal variations of sea surface temperature (SST), satellite-derived chlorophyll a (Chlsat) con-centration, and phytoplankton production (PP) along two 300-km long transects in the southernmost part of the California Current System, one off Cabo San Lázaro (TCSLa) and the other off Cabo San Lucas (TCSLu). Moderate Resolution Imaging Spectroradiometer (Aqua-MODIS) SST and Chlsat monthly composites and PP monthly composites were used for the 2003–2016 period. An “average year” was generated for each transect and each variable, as an approximation to the climatology. The Chlsat and PP values were higher in the inshore area than in the offshore area: 4.0 mg·m–3 and 4.5 g C·m–2·d–1, respectively, for the inshore area of TCSLa and 1.4 mg·m–3 and 1.8 g C·m–2·d–1, respectively, for the inshore area of TCSLu; ~0.1 mg·m–3 and 0.4 g C·m–2·d–1, respectively, for the offshore area of both transects. In general, SST showed minimum values (~17.0 ºC) in the inshore area and maximum values (~29.4 ºC) in the offshore area. Chlsat values in the coastal zone were higher on TCSLa than on TCSLu, but offshore Chlsat values were often higher on TCSLu than on TCSLa. Seasonal and interannual variations were observed on both transects, but the seasonal variations were dominant. The effects of “the Blob” in 2014 and of the 2015–2016 eastern Pacific type of El Niño were similarly strong off both capes but caused no collapse in phytoplankton biomass, which decreased to only approximately half the values for the non-El Niño years. The 2003 and 2010 central Pacific type of El Niño events also had strong impacts. The 2005 central Pacific type of El Niño had a strong impact on the biology of TCSLu, like the impact of the 2014 and 2015–2016 events, but not on the biology of TCSLa. The coastal dynamics in the California Current System show spatial variations; thus, seasonal and interannual events have different effects at different geographic locations.
Highlights
The California Current System (CCS) is a very large transitional area that forms the eastern boundary of the North Pacific Gyre, with the confluence of Subarctic Water, Tropical Surface Water, and Subtropical Surface Water (Hickey 1998)
The CCS is influenced by El Niño/Southern Oscillation (ENSO) events that are associated with an increase of sea surface temperature (SST) and a decrease of Chl and phytoplankton production (PP) (Putt and Prézelin 1985; Torres-Moye and Alvarez-Borrego 1987; Reid 1988; Lynn et al 1998; Kahru and Mitchell 2000, 2002)
SST maxima and minima occurred from August through December on TCSLa and in June, July, and December on the other off Cabo San Lucas (TCSLu)
Summary
The California Current System (CCS) is a very large transitional area that forms the eastern boundary of the North Pacific Gyre, with the confluence of Subarctic Water, Tropical Surface Water, and Subtropical Surface Water (Hickey 1998) It basically consists of a wide (>500 km) equatorward surface (up to 300 m depth) current and a poleward subsurface flow at the edge of the continental shelf (Lynn and Simpson 1987). In the CCS, wind-induced upwelling events, which show seasonal variability, bring cold, nutrient-rich waters along the coast, from Washington to Baja California (Huyer 1983) This results in phytoplankton biomass (chlorophyll a concentration, Chl) and phytoplankton production (PP) gradients, with high values in the inshore area and a clear decrease towards the offshore area (Fargion et al 1993, Arroyo-Loranca et al 2015). Events with anomalously low SSTs (La Niña) may have the opposite effect, with relatively high Chl and PP
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